The present invention relates to rotary power shaft couplings, and methods of joining two rotary shaft sections together in alignment.
It is known that two shaft ends can be joined together by the use of couplings if the shafts are equipped with coupling flanges. Various types of couplings may be used, such as rigid friction couplings, claw couplings and geared couplings. The rotational motion of the shafts is transferred between faces of the coupling flanges by the friction occuring between two portions of the coupling. The friction is generated by axial forces acting on the shafts. In order to provide for the transfer of a torque which is greater than the torque produced by friction, but without changing any shaft or coupling dimensions, the known friction couplings have been provided with additional shearing elements. The shearing elements are placed between the contacting surfaces of the coupling flanges and typically are in the form of toggle bolts, shear bushings, claws, radially extending shear bolts or wedges, and radial serrations.
Recent developments in the engineering of turbo-generators relating to improvements in the cooling of rotor windings as well as to the use of high-grade materials have suggested the need for generator shafts of a reduced diameter. The reduction in size of the shafts would also require the use of a coupling having a correspondingly smaller-dimension. The coupling, however, must provide a sufficient transfer of torque from the turbine shaft to the generator shaft.
The known couplings for shafts such as are described above have a particular disadvantage in that an offset is required in each coupling both to center the two shaft sections and to absorb the generated shearing forces. At operating speeds, the centrifugal forces generated by the rotation of the shafts may cause the offset in the first coupling flange to expand to a greater degree than the offset in the second flange. Accordingly, the coupling may slide with the expansion causing an eccentricity of the two shaft sections. The eccentricity results in a unbalancing of the rotors. Other known types of couplings are objectionable because they are costly to manufacture and require very accurate machining of the two coupling parts.
It is an object of the present invention to provide a simplified method for connecting two shafts together which does not require costly preparatory work.
It is a further object of the present invention to provide a method of joining shafts together in a manner which can be accomplished without any difficulty at the site of assembly, for example inside an assembled turbo-generator structure, and which will insure a maximum transfer of torque with a minimum shaft dimension.
The process of the present invention accomplishes these and other objects by means of a coupling that is made by depositing weld material of a low alloy steel on the opposing end faces of the shaft sections. The two shaft sections are then annealed by a thermal treatment which generates a minimum of stresses in the shaft sections. A welding groove is machined in the welded portion of each shaft section.
When it is desired to assemble the shaft sections together inside of the turbine and generator structure, a welding ring is inserted in a groove in one of the two shaft sections and the other shaft section is positioned in end-to-end abutting relation with the first shaft section, with the welding ring received in a corresponding groove in the second shaft section. The two shaft sections are then heated up to a temperature sufficient to cause fusion of a welding powder that is progressively deposited in the welding groove formed between the abutting ends of the two shaft sections. The welding powder is deposited in the welding groove while the two shaft sections are being rotated. The welded coupling is then allowed to cool.